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The OGLE Collection of Variable Stars. Over 15 000 δ Scuti Stars in the Large Magellanic Cloud

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Soszyński I. , Pietrukowicz P. , Udalski A. , Skowron J. , Szymański M. K. , Poleski R. , Skowron D. M. , Kozłowski S. , Mróz P. , Iwanek P. , Wrona M. , Ulaczyk K. , Rybicki K. , Gromadzki M. , Mróz M.

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tom Vol. 73, No. 2

105--126

EN

We present the OGLE collection of δ Scuti stars in the Large Magellanic Cloud and in its foreground. Our dataset encompasses a total of 15 256 objects, constituting the largest sample of extragalactic δ Sct stars published so far. In the case of 12 δ Sct pulsators, we detected additional eclipsing or ellipsoidal variations in their light curves. These are the first known candidates for binary systems containing δ Sct components beyond the Milky Way. We provide observational parameters for all variables, including pulsation periods, mean magnitudes, amplitudes, and Fourier coefficients, as well as long-term light curves in the I- and V-bands collected during the fourth phase of the OGLE project. We construct the period-luminosity (PL) diagram, in which fundamental-mode and first-overtone δ Sct stars form two nearly parallel ridges. The latter ridge is an extension of the PL relation obeyed by first-overtone classical Cepheids. The slopes of the PL relations for δ Sct variables are steeper than those for classical Cepheids, indicating that the continuous PL relation for first-overtone δ Sct variables and Cepheids is non-linear, exhibiting a break at a period of approximately 0.5 d. We also report the enhancement of the OGLE collection of Cepheids and RR Lyr stars with newly identified and reclassified objects, including pulsators contained in the recently published Gaia DR3 catalog of variable stars. As a by-product, we estimate the contamination rate in the Gaia DR3 catalogs of Cepheids and RR Lyr variables.

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Discovery and Observations of the Unusually Luminous Type-Defying II-P/II-L Supernova ASASSN-13co

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Holoien T. W.-S. , Prieto J. L. , Pejcha O. , Stanek Z. , Kochanek C. S. , Shappee B. J. , Grupe D. , Morrell N. , Thorstensen J. R. , Basu U. , Beacom J. F. , Bersier D. , Brimacombe J. , Davis A. B. , Pojmański G. , Skowron D. M.

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tom Vol. 66, No. 2

219--238

EN

We present photometric and spectroscopic observations of ASASSN-13co, an unusually luminous Type II supernova and the first core-collapse supernova discovered by the All-Sky Automated Survey for SuperNovae (ASAS-SN). First detection of the supernova was on UT 2013 August 29 and the data presented span roughly 3.5 months after discovery. We use the recently developed model by Pejcha and Prieto to model the multi-band light curves of ASASSN-13co and derive the bolometric luminosity curve. We compare ASASSN-13co to other Type II supernovae to show that it was unusually luminous for a Type II supernova and that it exhibited an atypical light curve shape that does not cleanly match that of either a standard Type II-L or Type II-P supernova.

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OGLE Collection of Star Clusters. New Objects in the Outskirts of the Large Magellanic Cloud

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Sitek M. , Szymański M. K. , Skowron D. M. , Udalski A. , Kostrzewa-Rutkowska Z. , Skowron J. , Karczmarek P. , Cieślar M. , Wyrzykowski Ł. , Kozłowski S. , Pietrukowicz P. , Soszyński I. , Mróz P. , Pawlak M. , Poleski R. , Ulaczyk K.

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tom Vol. 66, No. 3

255--267

EN

The Magellanic System (MS), consisting of the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) and the Magellanic Bridge (MBR), contains diverse sample of star clusters. Their spatial distribution, ages and chemical abundances may provide important information about the history of formation of the whole System. We use deep photometric maps derived from the images collected during the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV) to construct the most complete catalog of star clusters in the Large Magellanic Cloud using the homogeneous photometric data. In this paper we present the collection of star clusters found in the area of about 225 square degrees in the outer regions of the LMC. Our sample contains 679 visually identified star cluster candidates, 226 of which were not listed in any of the previously published catalogs. The new clusters are mainly young small open clusters or clusters similar to associations.

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Additional Galactic Cepheids from the OGLE Survey

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Soszyński I. , Udalski A. , Szymański M. K. , Pietrukowicz P. , Skowron J. , Skowron D. M. , Poleski R. , Kozłowski S. , Mróz P. , Ulaczyk K. , Rybicki K. , Iwanek P. , Wrona M. , Gromadzki M.

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tom Vol. 70, No. 2

101--119

EN

We report on the results of a comprehensive search for Cepheid variable stars in the fields photometrically monitored by the OGLE Galaxy Variability Survey. We identify 742 Cepheids not included in the first release of the OGLE Collection of Galactic Cepheids and reclassify several dozen previously published variables. The upgraded collection comprises 1974 classical, 1625 type II, and 119 anomalous Cepheids located in the area of about 3000 square degrees covering the disk and bulge of the Milky Way. We present the most interesting objects in our sample: an isolated group of long-period double-mode classical Cepheids pulsating in the fundamental mode and first overtone, the first known Galactic double-mode Cepheid with the second and third overtone excited, double-mode type II Cepheids, candidates for single-mode first-overtone BL Her stars, and Cepheids showing simultaneous eclipsing variability. We also discuss type II and anomalous Cepheids that are potential members of globular clusters.

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OGLE-ing the Magellanic System: Three-Dimensional Structure of the Clouds and the Bridge using RR Lyrae Stars

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Jacyszyn-Dobrzeniecka A. M. , Skowron D. M. , Mróz P. , Soszyński I. , Udalski A. , Pietrukowicz P. , Skowron J. , Poleski R. , Kozłowski S. , Wyrzykowski Ł. , Pawlak M. , Szymański M. K. , Ulaczyk K.

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tom Vol. 67, No. 1

1--35

EN

We present a three-dimensional analysis of a sample of 22 859 type ab RR Lyr stars in the Magellanic System from the OGLE-IV Collection of RR Lyr stars. The distance to each object was calculated based on its photometric metallicity and a theoretical relation between color, absolute magnitude and metallicity. The LMC RR Lyr distribution is very regular and does not show any substructures. We demonstrate that the bar found in previous studies may be an overdensity caused by blending and crowding effects. The halo is asymmetrical with a higher stellar density in its north-eastern area, which is also located closer to us. Triaxial ellipsoids were fitted to surfaces of a constant number density. Ellipsoids farther from the LMC center are less elongated and slightly rotated toward the SMC. The inclination and position angle change significantly with the $a$ axis size. The median axis ratio is 1:1.23:1.45. The RR Lyr distribution in the SMC has a very regular, ellipsoidal shape and does not show any substructures or asymmetries. All triaxial ellipsoids fitted to surfaces of a constant number density have virtually the same shape (axis ratio) and are elongated along the line-of-sight. The median axis ratio is 1:1.10:2.13. The inclination angle is very small and thus the position angle is not well defined. We present the distribution of RR Lyr stars in the Magellanic Bridge area, showing that the Magellanic Clouds' halos overlap. A comparison of the distributions of RR Lyr stars and Classical Cepheids shows that the former are significantly more spread and distributed regularly, while the latter are very clumped and form several distinct substructures.

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The OGLE Collection of Variable Stars. Classical, Type II, and Anomalous Cepheids toward the Galactic Center

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Soszyński I. , Udalski A. , Szymański M. K. , Wyrzykowski Ł. , Ulaczyk K. , Poleski R. , Pietrukowicz P. , Kozłowski S. , Skowron D. M. , Skowron J. , Mróz P. , Pawlak M. , Rybicki K. , Jacyszyn-Dobrzeniecka A.

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tom Vol. 67, No. 4

297--316

EN

We present a collection of classical, typeII, and anomalous Cepheids detected in the OGLE fields toward the Galactic center. The sample contains 87 classical Cepheids pulsating in one, two or three radial modes, 924 type II Cepheids divided into BL Her, W Vir, peculiar W Vir, and RV Tau stars, and 20 anomalous Cepheids - first such objects found in the Galactic bulge. Additionally, we upgrade the OGLE Collection of RR Lyr stars in the Galactic bulge by adding 828 newly identified variables. For all Cepheids and RRLyr stars, we publish time-series VI photometry obtained during the OGLE-IV project, from 2010 through 2017. We discuss basic properties of our classical pulsators: their spatial distribution, light curve morphology, period-luminosity relations, and position in the Petersen diagram. We present the most interesting individual objects in our collection: a typeII Cepheid with additional eclipsing modulation, WVir stars with the period doubling effect and the RVb phenomenon, a mode-switching RR Lyr star, and a triple-mode anomalous RRd star.

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Final Release of the OGLE Collection of Cepheids and RR Lyrae Stars in the Magellanic System. The Outer Regions

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Soszyński I. , Udalski A. , Szymański M. K. , Pietrukowicz P. , Skowron J. , Skowron D. M. , Poleski R. , Kozłowski S. , Mróz P. , Ulaczyk K. , Rybicki K. , Iwanek P. , Wrona M.

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tom Vol. 69, No. 2

87--99

EN

We present the final release of the OGLE collection of classical pulsators (Cepheids and RR Lyr stars) in the Large and Small Magellanic Clouds. The sky coverage has been increased from 670 to 765 square degrees compared to the previous edition of our collection. We also add some Cepheids and RR Lyr stars found by the Gaia team and reclassify three Cepheids. Ultimately, our collection consists of 9650 classical Cepheids, 343 type II Cepheids, 278 anomalous Cepheids, and 47 828 RR Lyr stars inside and toward the Magellanic System.

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The OGLE Collection of Variable Stars: Over 18 000 Rotating Variables toward the Galactic Bulge

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Iwanek P. , Soszyński I. , Stępień K. , Kozłowski S. , Skowron J. , Udalski A. , Szymański M. K. , Wrona M. , Pietrukowicz P. , Poleski R. , Mróz P. , Ulaczyk K. , Skowron D. M. , Gromadzki M. , Rybicki K. , Mróz M. J. , Ratajczak M.

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tom Vol. 74, No. 1

1--25

EN

Stellar rotation, a key factor influencing stellar structure and evolution, also drives magnetic activity, which is manifested as spots or flares on stellar surface. Here, we present a collection of 18 443 rotating variables located toward the Galactic bulge, identified in the photometric database of the Optical Gravitational Lensing Experiment (OGLE) project. These stars exhibit distinct magnetic activity, including starspots and flares. With this collection, we provide long-term, time-series photometry in Cousins I- and Johnson V-band obtained by OGLE since 1997, and basic observational parameters, i.e., equatorial coordinates, rotation periods, mean brightness, and brightness amplitudes in both bands. This is a unique dataset for studying stellar magnetic activity, including activity cycles.